kinetics simulation

Michaelis Menten sounds like you will not gonna extend your
problem-description to a PDE-system, therefore any math-package like
Maple, Mathematica or (!) Matlab are able to help you on.
However you might even think of very nice interfaces to build your ODE-sets
graphically, here I would recommend a Matlab-Simulink^ or Stella(=IThink)^^
software alot more packages of this sort exist but I don´t remember
their names...
Programs like Maple , Mathematica, and Matlab you might even get in your
neighbourly scientific-bookstore.
Cheers Tobias
^ = Mathworks
^^ = High Perfromance Systems (Hanover, NH)
_________________________________________________________________________
Tobias F. Christen
c/o Ciba Ltd
K-125.14.42
Ph 2.2423
4002 Basel (Switzerland)